Original subtitles

Now that we�ve look briefly at cabling

I�d like to explain how network devices operate.

And the first device that we're going to look at is hub

a hub is a layer 1 device in the OSI model and you would use a Cat5

unshielded twisted pair cable with an RJ-45 connector

to connect your laptop as an example to a port on a hub.

hubs aren't very popular today and have been superseded by

switches and I'll explain in a few minutes why.

But for now lets assume that you are connecting your PC to a hub. 10

It�s important that you understand how a hub operate 11

however because wireless operates in the same way, like a physical hub would. 12

So when your connected to a wireless network you�ll often encounter 13

the same issues that you would encounter when connecting to a physical hub. 14

So for now lets assume that you are connecting your PC physically to a hub 15

hubs have multiple ports and thus multiple devices 16

can be connected to a hub at the same time. 17

The number of ports available depends on the hub model 18

but as you can see in both of this examples 19

a hub has various ports that you can connect devices to. 20

So in this topology let�s assume that you have 4 devices connected to a hub 21

on ports 1 to 4, it's important to realize that a hub is a physical layer device. 22

It�s not intelligent and does not understand the frames going through it. 23

It's basically a multi port repeater and it will amplify 24

or repeat the frames that it receives on 1 port out of all other ports. 25

So it's once again simply a multi port repeater with no intelligence. 26

The physical topology of a hub is a star topology. 27

In a star topology you have a central device 28

which in this case is a hub and devices hanging off that central device 29

as spokes which resemble the spokes in the bicycle wheel. 30

Each spoke devices connected to the central device with its own cable and all 31

transmission or communications between devices are through the central device. 32

In other words if A wants to communicate with C the traffic will flow 33

through the hub and will not flow directly between the 2 devices. 34

There were some major advantages to using hubs and UTP rather than 10base2. 35

The first advantage is a cable break, if a cable broke in this topology 36

it would only affect device A and it would not affect the rest of the network. 37

In a 10base2 if a cable broke it would affect all devices in that network. 38

Here however, other devices such as C and B can still communicate 39

even though the cable is broken to device A. 40

Another advantages that you can extend distances easily. 41

A bus topology is limited in size in a 10baseT environment 42

such as this, the distance between a device such as A and the hub 43

needs to be 100 meters but you can extend the distance by adding another hub. 44

In other words you add another multiple repeater and repeat or regenerate 45

the signal to extend the distance of the network to distances greater than 100 meters. 46

So in this example, E could be 100 meters away from its hub 47

and the 2 hubs could be 50 meters apart. 48

So in this example we've extended the network 49

further than the restriction of a 100 meters. 50

So device E could be 100 meters from its hub 51

it could be a cable length a 50 meters between the 2 hubs 52

and A could be a 100 meters away from its hub. 53

A network now has a length of 250 meters 54

which is well over the limitation of a 100 meters. 55

Now their are restriction on the number of hubs 56

that you can daisy chain together, but the point is, it's possible 57

to extend the topology by adding more hubs and more devices to the network. 58

These were therefore great reasons to move away from 10base2 59

and 10base5 and implement UTP or untwisted pair networks using hubs. 60

Another advantage is that UTP cabling is cheaper and easier to manage 61

and therefore it became common to use 62

hubs and 10baseT rather than 10base2 or 10base5 in the past.